pH and Redox Dual-Response Disulfide Bond-Functionalized Red-Emitting Gold Nanoclusters for Monitoring the Contamination of Organophosphorus Pesticides in Foods

pH-responsive dual-emission carbon dots for the ratiometric detection of organophosphorus pesticides in Brassica chinensis and Hg2+ in water

Accurate and rapid monitoring of organophosphorus pesticides (OPs) residues is crucial for regulating food safety. Herein, dual-emission carbon dots (de-CDs) were fabricated for the ratiometric detection of OPs and Hg2+. The de-CDs exhibited two emission peaks at 678 and 485 nm when excited with visible light. Interestingly, the fluorescence at 678 nm was significantly quenched by Hg2+ mainly because of the static quenching effect, whereas that at 485 nm exhibited a slight change. More significantly, the quenched fluorescence of the de-CDs recovered remarkably after introducing omethoate, diazinon and malathion. Accordingly, the ratiometric detection of the three OPs and Hg2+ was achieved with high selectivity and robust performance. In addition, the OPs residues assay in Brassica chinensis was successfully performed with satisfactory results. This study not only provides an attractive tool for the simple and rapid assay of OPs but also offers new insights into the fabrication of multi-functional carbon dots.

A fluorescence ionic probe utilizing Cu2+ assisted competition for detecting glyphosate abused in green tea

Food fraud caused by the violation of glyphosate use in tea is frequently exposed, posing a potential health risk to consumers and undermining trust in food safety. In the work, an ionic fluorescent probe "[P66614] [4HQCA]-Cu2+ (PHQCA-Cu2+)" was constructed using Cu2+ and ionic liquids coordination through a competitive coordination strategy to detect glyphosate. This probe exhibited a prominent "turn-on" fluorescence response in glyphosate detection. PHQCA-Cu2+was destroyed by glyphosate with its strong coordination capability, and a new complex re-formed simultaneously between glyphosate and the Cu2+ in it, where Cu2+ served as an "invisible indicator" influencing fluorescence changes. Remarkably, PHQCA-Cu2+formed rapidly within 5 s, demonstrated exceptional sensitivity and selectivity, and satisfactory detection performance on paper strips impregnated withPHQCA-Cu2+.Importantly,PHQCA-Cu2+showed excellent recoveries in various green tea, which offered a viable method for identifying contaminated products from the supply chain quickly to enhance overall food safety surveillance.

Ionic liquid-enhanced silica aerogels for the specific extraction and detection of aflatoxin B1 coupled with a smartphone-based colorimetric biosensor

The polymer ionic liquid (1-allyl-3-butylimidazolium bromide) enhanced silica aerogel was modified onto the surface of stainless-steel mesh to immobilize aptamer-1 for the specific recognition of AFB1. The porous channels of silica aerogel could prevent the interference of macromolecules in food samples. Enzyme kinetic analysis showed that the MoS2/Au was an effective peroxidase mimic with a relatively low Michaelis constant (Km) value of 0.17 mM and a high catalytic rate of 3.87 × 10-8 mol (L·s)-1, which exhibited obvious superiority compared with horseradish peroxidase. The established "sandwich-structure" biosensor was coupled with the smartphone "Color Picker" application was used to detect AFB1 with a wide linear range (1-100 ng mL-1) and low detection limit (0.25 ng mL-1). The anti-interference ability of the established biosensor was evaluated by adding different concentrations of standards in corn, peanut, and wheat and matrix effects were 90.84-106.11 %. The results showed that this method demonstrated high specificity, sensitivity, rapidity and low interference in food samples.

Triple modal aptasensor arrays driven by CHA-mediated DNAzyme for signal-amplified atrazine pesticide accumulation monitoring in agricultural crops

Developing sensors with high selectivity and sensitivity is of great significance for pesticide analysis in environmental assessment. Herein, a versatile three-way sensor array was designed for the detection of the pesticide atrazine, based on the integration of catalytic hairpin assembly (CHA) amplification and three-mode signal transducers. With atrazine, CHA was triggered to generate abundant G-quadruplex. The produced G-quadruplex hybrid could assemble with thioflavin T (TFT) or hemin to mimic enzyme and induce the fluorescence enhancement by TFT, or the colorimetric increase by the oxidized chromogenic substrate and the naked-eye color change by inhibiting the L-cysteine-mediated aggregation of gold nanoparticles. A distinctive three-mode array was successfully constructed with convenience, on-site accessibility and high sensitivity for enzyme-free practical analysis of atrazine. It is also effective and reliable for analyzing real samples including paddy water, paddy soil and polished rice. The detection limits for atrazine were as low as 7.4 pg/mL by colorimetric observation and 0.25 pg/mL by fluorescent detection. Furthermore, the array was exploited to monitor the residue, distribution and bioaccumulation of atrazine in maize and rice for food security and environmental assessment. Hence, this work presented a versatile example for sensitive and on-site all-in-one pesticide analysis arrays with multiple signal report modes.

Fluorescent chemosensors facilitate the visualization of plant health and their living environment in sustainable agriculture

Globally, 91% of plant production encounters diverse environmental stresses that adversely affect their growth, leading to severe yield losses of 50-60%. In this case, monitoring the connection between the environment and plant health can balance population demands with environmental protection and resource distribution. Fluorescent chemosensors have shown great progress in monitoring the health and environment of plants due to their high sensitivity and biocompatibility. However, to date, no comprehensive analysis and systematic summary of fluorescent chemosensors used in monitoring the correlation between plant health and their environment have been reported. Thus, herein, we summarize the current fluorescent chemosensors ranging from their design strategies to applications in monitoring plant-environment interaction processes. First, we highlight the types of fluorescent chemosensors with design strategies to resolve the bottlenecks encountered in monitoring the health and living environment of plants. In addition, the applications of fluorescent small-molecule, nano and supramolecular chemosensors in the visualization of the health and living environment of plants are discussed. Finally, the major challenges and perspectives in this field are presented. This work will provide guidance for the design of efficient fluorescent chemosensors to monitor plant health, and then promote sustainable agricultural development.

Ultrathin-FeOOH-coated MnO2 nanozyme with enhanced catalase-like and oxidase-like activities for photoelectrochemical and colorimetric detection of organophosphorus pesticides

Herein, we develop a dual-mode biosensor for photoelectrochemical and colorimetric detection of organophosphate pesticides (OPPs) based on ultrathin-FeOOH-coated MnO2 (MO@FHO) nanozyme. In this biosensor, OPPs can inhibit the alkaline phosphatase (ALP) activity and hinder the dephosphorylation of l-ascorbic acid-2-phosphate, preventing the decomposition of MO@FHO nanozyme and inducing both a photoelectrochemical (PEC) signal and the colorimetric change. The MO@FHO nanozyme not only possesses an enhanced catalase-like activity to degrade H2O2 for the generation of an improved cathodic photocurrent, but also exhibits an excellent oxidase-like activity to oxidize 3,3,5,5-tetramethylbenzidine with high catalytic efficiency. This biosensor displays a detection limit of 50 pmol/L for the PEC mode and a detection limit of 0.8 nmol/L for the colorimetric mode. Moreover, this biosensor exhibits excellent performance in complex biological matrices, and the smartphone-based visual sensing platform facilitates rapid and sensitive detection of OPPs, holding promising applications in food safety monitoring, and on-site detection.

Construction of logic gate computation for the assay of the nerve agent sarin based on an AChE-based dual-channel sensing system

Nerve agents have posed a huge threat to national and human security, and their sensitive detection is crucial. Herein, based on the oxidation of Ce4+ and the aggregation-induced emission (AIE) of glutathione-protected gold nanoclusters (GSH-Au NCs), a cascade reaction was designed to prepare oxidized 3,3',5,5'-tetramethylbenzidine (oxTMB) and GSH-Au NCs crosslinked by Ce3+ (Ce3+-GSH-Au NCs). oxTMB had a broad UV-visible absorption range (500-700 nm) and was capable of quenching the fluorescence of Ce3+-GSH-Au NCs at 590 nm through the internal filtration effect (IFE). Thiocholine (TCh), the hydrolysis product of acetylthiocholine chloride (ATCl) catalyzed by acetylcholinesterase (AChE), reduced oxTMB completely, resulting in a decrease in the absorption of oxTMB and the recovery of IFE-quenched fluorescence of Ce3+-GSH-Au NCs. Nerve agent sarin (GB) hindered the production of TCh and the reduction of oxTMB by inhibiting the AChE activity, leading to the fluorescence of Ce3+-GSH-Au NCs being quenched again. The dual-output sensing system (AChE + ATCl + oxTMB + Ce3+-GSH-Au NCs) exhibited a low limit of detection to GB (2.46 nM for colorimetry and 1.18 nM for fluorimetry) and excellent selectivity toward common interferences being unable to inhibit AChE. Moreover, the intelligent logic gate constructed based on the sensing system showed promising applications in the field of smart sensing of nerve agents.

Portable hydrogel kit based on Michael addition reaction for (E)-2-hexenal gas detection

Plants exhibit rapid responses to biotic and abiotic stresses by releasing a range of volatile organic compounds (VOCs). Monitoring changes in these VOCs holds the potential for the early detection of plant diseases. This study proposes a method for identifying late blight in potatoes based on the detection of (E)-2-hexenal, one of the major VOC markers released during plant infection by Phytophthora infestans. By combining the Michael addition reaction with cysteine-mediated etching of aggregation-induced emission gold nanoclusters (Au NCs), we have developed a portable hydrogel kit for on-site detection of (E)-2-hexenal. The Michael addition reaction between (E)-2-hexenal and cysteine effectively alleviates the etching of cysteine-mediated Au NCs, leading to a distinct fluorescence color change in the Au NCs, enabling a detection limit of 0.61 ppm. Utilizing the superior loading and diffusion characteristics of the three-dimensional structure of agarose hydrogel, our sensor demonstrated exceptional performance in terms of sensitivity, selectivity, reaction time, and ease of use. Moreover, quantitative measurement of (E)-2-hexenal was made easier by using ImageJ software to transform fluorescent images from the hydrogel kit into digital data. Such method was effectively used for the early detection of potato late blight. This study presents a low-cost, portable fluorescent analytical tool, offering a new avenue for on-site detection of plant diseases.

Anchoring Au nanoclusters into coordination polymers: A novel approach toward ATP detection and its application

Adenosine triphosphate (ATP) is the main source of energy required for all life activities and is used as a biomarker for diseases such as cancer. It is of great significance to design a novel fluorescent probe with favorable performance for monitoring the changes of ATP concentration. Herein, a fluorescence probe named ZnCPs@AuNCs for ATP sensing was designed and fabricated by integrating AuNCs into ZnCPs. The emission intensity of AuNCs was greatly enhanced upon the formation of the ZnCPs@AuNCs nanocomposites, which may be attributed to ZnCPs restricting the molecular motion of AuNCs. Upon the introduction of ATP, the fluorescence intensity at 564 nm of ZnCPs@AuNCs is quenched. According to this phenomenon, a sensitive and reliable ATP sensing platform was established. Moreover, ZnCPs@AuNCs were incorporated into a poly (vinyl alcohol) matrix for the fabrication of fluorescent film, which exhibited solid-state fluorescence. Inspired by the remarkable fluorescent properties of ZnCPs@AuNCs, the fluorescent hydrogel was prepared by mixing ZnCPs@AuNCs with κ-carrageenan, which demonstrated a response to ATP and favorable self-healing ability. This work presents a perspective of ZnCPs@AuNCs in multiple applications such as biosensing, fluorescent film, and hydrogel construction.

Analyte-perturbed balance between reducibility and fluorescence of Ti3C2 MXene quantum dots for label-free, dual-mode detection of silver ions

BACKGROUND

As an emerging and attractive low-dimensional functional materials, Ti3C2 MXene quantum dots (QDs) enlarge the toolbox of fluorescence sensing. However, monochromatic fluorescence, which only provide one single signal, is often beset by challenges such as false-positive readouts and limitations in selectivity. Consequently, to improve the sensing accuracy by means of cross-verified dual-signal authentication, the endeavor to engineer dual-mode nanoprobes based on Ti3C2 QDs, incorporating both the capability of fluorescence and an alternative sensing mechanism, emerges as a compelling avenue.

RESULTS

Here, based on the alterations in colorimetric and fluorescent signals of Ti3C2 QDs with the addition of Ag+, we propose a dual-mode sensor obviating the necessity for nanoprobe labeling. Owing to the decent reducibility of Ti3C2 QDs, Ag+ is adsorbed and reduced, resulting in the generation of plasmonic Ag nanoparticles (NPs), which simultaneously trigger colorimetric responses of the solution and enhance the fluorescent emission of Ti3C2 QDs. The confluence of colorimetry and fluorometry within this strategy optimally harnesses the modulating role of the acquired Ag NPs on the reducing capability and fluorescence characteristics of Ti3C2 QDs. The equilibrium imparts versatility and promising prospects to this analyte-triggered label-free method, which enables a remarkable specificity and an excellent detecting limit (0.45 μM) for Ag+.

SIGNIFICANCE

The balance between reducibility and fluorescence of Ti3C2 QDs for dual-mode detection is inventively demonstrated. With the exemplification of a direct influence of both features of the nanoprobe via the introduction of analytes, this study opens the feasibility of the analyte-perturbed felicitous equilibrium, which endows label-free methods with versatility and promising prospects. This design may evoke more biosensing strategies with the function of double-signal mutual verification.

Chameleon-like Response Mechanism of Gold-Silver Bimetallic Nanoclusters Stimulated by Sulfur Ions and Their Application in Visual Fluorescence Sensing

Herein, 2-mercapto-5-benzimidazolesulfonate acid sodium salt dihydrate (MBZS)-protected gold-silver bimetallic nanoclusters, named MBZS-AuAg NCs, were synthesized. Interestingly, we found that MBZS-AuAg NCs solutions can exhibit different fluorescence color changes under sulfide stimulation. A series of modern analytical testing techniques were used to explore the interaction mechanism between MBZS-AuAg NCs and sulfide. Sulfide ions can not only cause MBZS-AuAg NCs to exhibit rich fluorescence color changes similar to those of a chameleon but also have four linear relationships between the response intensity and sulfide concentration. A wide-range sulfide fluorescence sensing platform was constructed based on four linear segments with different fluorescence color responses. This sensing platform can be directly used for the determination of S2- with a detection limit as low as 11 nM. The portable test paper based on MBZS-AuAg NCs can realize the visual and rapid detection of gaseous hydrogen sulfide with a detection limit of 100 ppb (v/v). The wide detection range of the proposed method not only allows it to be used as an alternative method for sulfide detection in environmental samples but also has potential applications in the rapid detection and early warning of hydrogen sulfide gas in industrial and mining scenarios.

Carboxymethyl potato starch hydrogels encapsulated cyclodextrin metal-organic frameworks for enantioselective loading of S-naproxen and its programmed release

A natural polysaccharide-based vehicle is facilely prepared for enantioselective loading of S-naproxen (S-NPX) and its programmed release. Cyclodextrin metal-organic frameworks (CD-MOF) are synthesized through the coordination of K+ with γ-cyclodextrin (γ-CD). Compared with R-NPX, the CD-MOF preferably combines with S-NPX, which can be confirmed by the thermodynamic calculations. The S-NPX loaded CD-MOF (CD-MOF-S-NPX) is grafted with disulfide bond (-S-S-) to improve its hydrophobicity, and the loaded S-NPX is further encapsulated in the chiral cavity of γ-CD by carboxymethyl potato starch (CPS) hydrogels. The intermolecular hydrogen bonding of the CPS hydrogels is prone to be destroyed in mildly basic media (∼pH 8.0), resulting in the swelling of the hydrogels; the -S-S- linkage in the vehicle can be cleaved in the presence of glutathione (GSH), leading to the collapse of the CD-MOF. Therefore, the programmed release of S-NPX can be achieved. Also in this work, the release kinetics is investigated, and the results indicate that the release of S-NPX is controlled by the Higuchi model.

Anchoring copper nanoclusters to Al2O3 microsphere for dual-mode analysis of N-acetyl-β-D-glucosaminidase and information encryption

Herein, we attempted to confine copper nanoclusters (CuNCs) with alumina (Al2O3) as the matrix (Al2O3@CuNCs), which effectively circumvented the drawbacks of CuNCs (such as weak photoluminescence and low quantum yield). Al2O3@CuNCs demonstrated sensitive response to p-nitrophenol, the catalytic product of N-acetyl-β-D-glucosaminidase (NAG) on account of the inner filter effect and dynamic quenching effect. In light of this, a novel assay was created to identify NAG, a critical indicator of diabetic nephropathy. Additionally, a portable and instrument-free sensing platform mainly consisting of a smartphone, a cuvette, a cuvette holder, a dark box and a 365 nm UV lamp was developed for the quantitative detection of NAG. The as-prepared material was also utilized in anti-counterfeiting and information encryption based on their excellent optical properties and sensitive response to the catalyzed product of NAG. This work advanced potential applications of CuNCs composites in the areas of portable, multi-mode biosensing, anti-counterfeiting and information encryption.

Active site engineering of Zn-doped mesoporous ceria toward highly efficient organophosphorus hydrolase-mimicking nanozyme

Hydrolase-mimicking nanozymes have received increasing attention in recent years, but the effective rational design and development of these materials has not been realized, as they are not at present considered a critical research target. Herein, we report that Zn-doped mesoporous ceria (Zn-m-ceria) engineered to have an abundance of two different active sites with different functions-one that allows both co-adsorption binding of organophosphate (OP) and water and another that serves as a general base-has significant organophosphorus hydrolase (OPH)-like catalytic activity. Specifically, Zn-m-ceria exhibits a catalytic efficiency over 75- and 25-fold higher than those of m-ceria and natural OPH, respectively. First-principles calculations reveal the importance of Zn for the OPH-mimicking activity of the material, promoting substrate adsorption and proton-binding. The OPH-like Zn-m-ceria catalyst is successfully applied to detect a model OP, methyl paraoxon, in spiked tap water samples with excellent sensitivity, stability, and detection precision. We expect that these findings will promote research based on the rational engineering of the active site of nanozymes and efficient strategies for obtaining a diverse range of catalysts that mimic natural enzymes, and hence the utilization in real-world applications of enzyme-mimicking catalysts with properties superior to their natural analogs should follow.

Electrochemiluminescence enhanced by isolating ACQphores in imine-linked covalent organic framework for organophosphorus pesticide assay

Most of covalent organic frameworks (COFs) are non or weakly emissive due to either the molecular thermal motion-mediated energy dissipation or the aggregation-caused quenching (ACQ) effect. Herein, we synthesize an imine-linked COF (TFPPy-TPh-COF) with high electrochemiluminescence (ECL) emission and the capability of eliminating the ACQ effect and further construct an ECL sensor for malathion detection. The imine-linked COF is obtained by the condensation reaction of (1,1':3',1″-terphenyl)-4,4″-diamine (TPh) and 1,3,6,8-tetrakis(p-formylphenyl)pyrene (TFPPy), and it has higher ECL efficiency than TFPPy aggregates due to the separation of ACQ luminophores (i.e., TFPPy) from each other by TPh and the restriction of intramolecular motions of TFPPy and TPh to reduce the nonradiative decay. The efficient quenching of ECL is achieved by electrochemiluminescence resonance energy transfer (ERET) from the excited state of the TFPPy-TPh-COF to zeolite imidazolate framework-8 (ZIF-8) and the steric hindrance of ZIF-8. Acetylcholinesterase (AChE) can enzymatically hydrolyze acetylcholine (ACh) to generate acetic acid. The resultant acetic acid can trigger the dissolution of ZIF-8 to produce an enhanced ECL signal. Malathion as an organophosphorus pesticide serves as an AChE inhibitor to prevent the production of acetic acid, inducing the decrease of ECL signal. This sensor displays a limit of detection (LOD) of 2.44 pg/mL and a wide dynamic detection range of 0.01-1000 ng/mL. Furthermore, it can be used to detect other organophosphates pesticides (e.g., methidathion, chlorpyrifos, and paraoxon) and measure malathion in real samples (i.e., pakchoi, lettuce, and apples).

Glucose oxidation induced pH stimuli response controlled release electrochemiluminescence biosensor for ultrasensitive detection of CYFRA 21-1

Herein, a self on electrochemiluminescence (ECL) biosensor was constructed by pH stimuli response controlled release strategy, in which SiO2-PEI as the carrier, BSA/luminol-Ab2 as the encapsulated substance, gold nanoparticles (Au NPs) as the blocking cap, glucose as the inducer. In addition, CeO2-Au was used as catalyst, which generated more O2•- to increase the ECL signal. Under the action of voltage, the glucose was oxidized to gluconic acid, which induced the pH to decrease accordingly. Therefore, Au NPs were stimulated to fall from the surface of SiO2-PEI, releasing the BSA/luminol-Ab2 to realize self on mode. With such design, the constructed self on ECL biosensor owned an ultrasensitive detection capacity of CYFRA 21-1, showing an excellent linear relationship in the range of 0.001-100000 ng/L and 0.4 fg/mL low limit of detection (LOD). It provided an innovative idea for the biosensor construction to clinical detection of lung cancer.

Optical nanosensors based on noble metal nanoclusters for detecting food contaminants: A review

Food contaminants present a significant threat to public health. In response to escalating global concerns regarding food safety, there is a growing demand for straightforward, rapid, and sensitive detection technologies. Noble metal nanoclusters (NMNCs) have garnered considerable attention due to their superior attributes compared to other optical materials. These attributes include high catalytic activity, excellent biocompatibility, and outstanding photoluminescence properties. These features render NMNCs promising candidates for crafting nanosensors for food contaminant detection, offering the potential for the development of uncomplicated, swift, sensitive, user-friendly, and cost-effective detection approaches. This review investigates optical nanosensors based on NMNCs, including the synthesis methodologies of NMNCs, sensing strategies, and their applications in detecting food contaminants. Furthermore, it involves a comparative assessment of the applications of NMNCs in optical sensing and their performance. Ultimately, this paper imparts fresh perspectives on the forthcoming challenges. Hitherto, optical (particularly fluorescent) nanosensors founded on NMNCs have demonstrated exceptional sensing capabilities in the realm of food contaminant detection. To enhance sensing performance, future research should prioritize atomically precise NMNCs synthesis, augmentation of catalytic activity and optical properties, development of high-throughput and multimode sensing, integration of NMNCs with microfluidic devices, and the optimization of NMNCs storage, shelf life, and transportation conditions.

Bifunctional TiO2 Nanoflower-Induced H4TCBPE Aggregation Enhanced Electrochemiluminescence for an Ultrasensitive Assay of Organophosphorus

In this work, the aggregation-induced emission ligand 1,1,2,2-tetra(4-carboxylbiphenyl)ethylene (H4TCBPE) was rigidified in the Ti-O network to form novel electrochemiluminescence (ECL) emitter H4TCBPE-TiO2 nanospheres, which acted as an effective ECL emitter to construct an "on-off" ECL biosensor for ultrasensitive detection of malathion (Mal). H4TCBPE-TiO2 exhibited excellent ECL responses due to the Ti-O network that can restrict the intramolecular free motions within H4TCBPE and then reduce the nonradiative relaxation. Moreover, TiO2 can act as an ECL co-reaction accelerator to promote the generation of sulfate radical anion (SO4•-), which interacts with H4TCBPE in the Ti-O network to produce enhanced ECL response. In the presence of Mal, numerous ligated probes (probe 1 to probe 2, P1-P2) were formed and released by copper-free click nucleic acid ligation reaction, which then hybridized with hairpin probe 1 (H1)-modified H4TCBPE-TiO2-based electrode surface. The P1-P2 probes can initiate the target-assisted terminal deoxynucleoside transferase (TdTase) extended reaction to produce long tails of deoxyadenine with abundant biotin, which can load numerous streptavidin-functionalized ferrocenedicarboxylic acid polymer (SA-PFc), causing quenching of the ECL signal. Thus, the ultrasensitive ECL biosensor based on H4TCBPE-TiO2 ECL emitter and click chemistry-actuated TdTase amplification strategy presents a desirable range from 0.001 to 100 ng/mL and a detection limit low to 9.9 fg/mL. Overall, this work has paved an avenue for the development of novel ECL emitters, which has opened up new prospects for ECL biosensing.

Synergetic-effect-enhanced electrochemiluminescence of zein-protected Au-Ag bimetallic nanoclusters for CA15-3 detection

In this work, a sandwich-type electrochemiluminescence (ECL) system was constructed for the detection of CA15-3. Gold-silver bimetallic nanoclusters (Au-Ag BNCs) with zein as a protective ligand were synthesized, and the excellent ECL performance of this material was demonstrated for the first time. Zein carrying a variety of groups that ligated with Au-Ag BNCs, forming a protective shell of zein, effectively prevented clusters from aggregating or growing into larger nanoparticles. The synergistic effect of the bimetal promotes the ECL emission, making this nanoscale material an ideal ECL probe. GO-PANI, which effectively promoting the production of sulfate radicals of the co-reactant and significantly increasing the ECL strength, was a good sensing platform for antibody immobilization. Consequently, we constructed an ECL sensor with GO-PANI as the sensing platform and Au-Ag BNCs@zein as the ECL probe, with a detection range of 0.001-100 U mL-1 and a detection limit of 0.0003 U mL-1, provided a strong support for the sensor for future CA15-3 detection applications.

Dual-Mode Gold Nanocluster-Based Nanoprobe Platform for Two-Photon Fluorescence Imaging and Fluorescence Lifetime Imaging of Intracellular Endogenous miRNA

Bioimaging is widely used in various fields of modern medicine. Fluorescence imaging has the advantages of high sensitivity, high selectivity, noninvasiveness, in situ imaging, and so on. However, one-photon (OP) fluorescence imaging has problems, such as low tissue penetration depth and low spatiotemporal resolution. These disadvantages can be solved by two-photon (TP) fluorescence imaging. However, TP imaging still uses fluorescence intensity as a signal. The complexity of organisms will inevitably affect the change of fluorescence intensity, cause false-positive signals, and affect the accuracy of the results obtained. Fluorescence lifetime imaging (FLIM) is different from other kinds of fluorescence imaging, which is an intrinsic property of the material and independent of the material concentration and fluorescence intensity. FLIM can effectively avoid the fluctuation of TP imaging based on fluorescence intensity and the interference of autofluorescence. Therefore, based on silica-coated gold nanoclusters (AuNCs@SiO2) combined with nucleic acid probes, the dual-mode nanoprobe platform was constructed for TP and FLIM imaging of intracellular endogenous miRNA-21 for the first time. First, the dual-mode nanoprobe used a dual fluorescence quencher of BHQ2 and graphene oxide (GO), which has a high signal-to-noise ratio and anti-interference. Second, the dual-mode nanoprobe can detect miR-21 with high sensitivity and selectivity in vitro, with a detection limit of 0.91 nM. Finally, the dual-mode nanoprobes performed satisfactory TP fluorescence imaging (330.0 μm penetration depth) and FLIM (τave = 50.0 ns) of endogenous miR-21 in living cells and tissues. The dual-mode platforms have promising applications in miRNA-based early detection and therapy and hold much promise for improving clinical efficacy.

Fluorescent Features and Applicable Biosensing of a Core-Shell Ag Nanocluster Shielded by a DNA Tetrahedral Nanocage

The DNA frame structure as a natural shell to stably shield the sequence-templated Ag nanocluster core (csAgNC) is intriguing yet challenging for applicable fluorescence biosensing, for which the elaborate programming of a cluster scaffold inside a DNA-based cage to guide csAgNC nucleation might be crucial. Herein, we report the first design of a symmetric tetrahedral DNA nanocage (TDC) that was self-assembled in a one-pot process using a C-rich csAgNC template strand and four single strands. Inside the as-constructed soft TDC architecture, the template sequence was logically bridged from one side to another, not in the same face, thereby guiding the in situ synthesis of emissive csAgNC. Because of the strong electron-repulsive capability of the negatively charged TDC, the as-formed csAgNC displayed significantly improved fluorescence stability and superb spectral behavior. By incorporating the recognizable modules of targeted microRNAs (miRNAs) in one vertex of the TDC, an updated TDC (uTDC) biosensing platform was established via the photoinduced electron transfer effect between the emissive csAgNC reporter and hemin/G-quadruplex (hG4) conjugate. Because of the target-interrupted csAgNC switching in three states with the spatial proximity and separation to hG4, an "on-off-on" fluorescing signal response was executed, thus achieving a wide linear range to miRNAs and a limit of detection down to picomoles. Without complicated chemical modifications, this simpler and more cost-effective strategy offered accurate cell imaging of miRNAs, further suggesting possible therapeutic applications.

Construction of a Label-Free Ratiometric Biosensor Based on Target Recycling Amplification and Hg-ZnSe QDs for Assay of BChE and OPs

Herein, we constructed a label-free ratiometric fluorescence biosensing strategy for the determination of butyrylcholinesterase (BChE) activity and organophosphorus (OPs) concentration. BChE promoted the hydrolysis of iodized s-butyrylthiocholine (BTCh) into a reducing substance thiocholine, which can decompose CoOOH nanosheets (CoOOH NSs) to Co2+. Subsequently, the single-stranded DNA (ssDNA) on the surface of CoOOH NSs was released. Then, ssDNA hybridized with hairpin DNA (h-DNA) and triggered the target recycling amplification process, producing large amounts of G-quadruplex. After adding thioflavin T (ThT), the target BChE was converted into activatable G-quadruplex/ThT with an amplified yellow fluorescence signal. The addition of OPs could significantly inhibit the hydrolysis of BTCh by BChE and thus unable to produce the yellow fluorescence G-quadruplex/ThT complex. Throughout the entire process, the fluorescence intensity of Hg-ZnSe QDs as a reference signal remained unchanged at 630 nm. Furthermore, this work provided an effective approach for detecting the BChE activity in serum samples and OPs in fruits and vegetables.

Guar gum-enhanced emission of gold nanoclusters for α-glucosidase activity detection and anti-diabetic agents screening in plant extracts

The development of efficient fluorescent methods for α-glucosidase (α-Glu) detection and α-Glu inhibitor screening plays a critical role in the therapy of type 2 diabetes (T2D). Herein, guar gum (GG), a high-abundant and non-toxic natural polymer originated from the seeds of a drought-tolerant plant, Cyamposis tetragonolobus, was found to be able to enhance the fluorescence emission of gold nanoclusters (AuNCs) probe. The emission enhancement effect was achieved by using GG at very low concentrations (<1.0 wt%) and presented in a viscosity-dependent manner through increasing solvent reorientation time and inhibiting intramolecular motions of AuNCs. Furthermore, the enhanced emission of the AuNCs was quenched by Fe³⁺via dynamic quenching and then restored by α-Glu. Accordingly, a fluorimetric method was proposed for the determination of α-Glu. Owing to the fluorescence enhancement effect of GG on the AuNCs probe, the detection limit of the approach was 0.13 U L^-1 and the detection range was up to 5 orders of magnitude from 0.2 to 4000 U L^-1, which was much better than most current α-Glu detection methods. The approach was further applied to α-Glu inhibitors screening from natural plant extracts, providing great prospects for the prevention and treatment of T2D.

Facile preparation of bimetallic Au-Cu nanoclusters as fluorescent nanoprobes for sensitive detection of Cr3+ and S2O82- ions

Metallic nanoclusters (NCs) have attracted special attention from researchers due to their interesting optical properties. In this experiment, we proposed a facile one-step method for the synthesis of bimetallic gold-copper nanoclusters (AuCuNCs). The prepared AuCuNCs were characterized by fluorescence spectroscopy (FL), UV-vis absorption spectrum, transmission electron microscopy (TEM), etc. The emission peak of the prepared AuCuNCs was located at 455 nm and showed blue luminescence under the excitation of 365 nm UV light. Furthermore, after the addition of Cr³⁺ and S₂O₈^2- ions, the FL emission intensity of AuCuNCs was significantly reduced at 455 nm and there was a color change of diminished blue luminescence under UV lamp. The AuCuNCs exhibited excellent linearity and sensitivity for the detection of Cr³⁺ and S₂O₈^2- ions. The limits of detection (LOD) for the Cr³⁺ and S₂O₈^2- ions were calculated to be 1.5 and 0.037 μM, respectively. Finally, the recoveries of Cr³⁺ and S₂O₈^2- ions in Runxi Lake and tap water were measured by standard addition recovery test and were 96.66 ∼ 116.29 %, 95.75 ∼ 119.4 %.

Identification of multi-component metal ion mixtures in complex systems using fluorescence sensor arrays

The growing co-contamination of multiple metal ions seriously influences human health due to their synergistic and additive toxicological effects, whereas the rapid discrimination of multiple heavy metal ions in complex aquatic systems remains a major challenge. Herein, a high- throughput fluorescence sensor array was fabricated based on three gold nanoclusters (GSH-Au NCs, OVA-Au NCs, and BSA-Au NCs) for the direct identification and quantification of seven heavy metal ions (Pb²⁺, Fe³⁺, Cu²⁺, Co²⁺, Ag⁺, Hg²⁺ and As³⁺) from environmental waters without sample pretreatment other than filtration. At the detection system, three gold nanoclusters with various ligands possessed distinct binding capacities against metal ions and induced aggregation-induced fluorescence enhancement and quenching, resulting in a unique pattern of fluorescence variations. Meanwhile, integrated the collected fluorescence fingerprints with linear discriminant analysis (LDA) and hierarchical cluster analysis (HCA), a discrete database was obtained for the accurate recognition and sensitive detection of metal ions. Under the optimized conditions, the limit of detection (LOD) of the proposed fluorescence sensor array for metal ions detection at nM concentration level along with a satisfactory accuracy. Importantly, our study indicated that the fluorescence sensor array could be widely used as a general platform in environmental monitoring against multiple targets at low concentrations.

A dual-signal fluorometric and colorimetric sensing platform based on gold-platinum bimetallic nanoclusters for the determination of β-galactosidase activity

Herein, a novel dual-signal sensing system for the determination of β-galactosidase (β-Gal) activity was established, which was based on a dual-emission probe assembled from gold-platinum bimetallic nanoclusters (Au-Pt NCs) and rhodamine B. Under the catalysis of β-Gal, 4-nitrophenyl β-D-galactopyranoside (PNPG) was rapidly hydrolyzed to generate p-nitrophenol (PNP), which has an obvious UV absorption peak at 400 nm. The hydrolyzed product PNP can quench the fluorescence of Au-Pt NCs effectively by inner filter effect (IFE), and PNP had no impact on the fluorescence of rhodamine B, which will change the emission intensity ratio of Au-Pt NCs and rhodamine B. Therefore, the ratiometric fluorescent and colorimetric dual-signal sensor based on Au-Pt NCs and rhodamine B was successfully constructed for sensitive detection of β-Gal activity. The linear detection range for the ratiometric fluorescence and colorimetric methods were 2.5-25 U/L and 15-55 U/L with detection limits of 1.2 U/L and 5.2 U/L, respectively. The developed assay method has been used for quantitative detection of β-Gal in spiked serum samples and showed good performance. And the detection platform has high reliability and excellent selectivity, which opens a new avenue for the further application of Au-Pt NCs in chemical sensing and biological analysis.

Near-infrared-excitable acetylcholinesterase-activated fluorescent probe for sensitive and anti-interference detection of pesticides in colored food

The development of a common and anti-interference acetylcholinesterase (AChE) inhibition assay for plant-originated food samples has been of great challenge because of the prevalent and strong signal interferences from natural pigments. Plant pigments normally exhibit non-negligible absorbance in the UV-visible region. As a result, the signals of a typical near-infrared (NIR) fluorescent probe could be disturbed through primary inner filter effect if it is excited by UV-visible light during plant sample analysis. In this work, an NIR-excitable AChE-activated fluorescent probe was biomimetically designed and synthesized. And the NIR-excitation strategy was utilized for the anti-interference detection of organophosphate and carbamate pesticides in colored samples with this probe. Sensitive and rapid response to AChE and pesticides was achieved due to the high affinity of the biomimetic recognition unit in the probe. The limits of detection for four representative pesticides including dichlorvos, carbofuran, chlorpyrifos and methamidophos reached 0.0186 μg/L, 2.20 μg/L, 12.3 μg/L and 13.6 μg/L, respectively. Most importantly, fluorescent response to pesticide contents could be accurately measured in the coexistence of different plant pigments by this probe, and the measured results showed completely irrelevance to the plant pigments and their colors. Taking advantage of such probe, the new developed AChE inhibition assay showed good sensitivity and anti-interference ability in the detection of organophosphate and carbamate pesticides in real samples.

IrO2 clusters loaded on dendritic mesoporous silica nanospheres with superior peroxidase-like activity for sensitive detection of acetylcholinesterase and its inhibitors

Nanomaterials-based enzyme mimics (nanozymes), by simulating enzyme catalysis, have shown potential in numerous biocatalytic applications, but nanozymes face significant challenges of catalytic activity and reusability that may restrict their practical uses. Herein, we report facile fabrication of surface-clean IrO₂ clusters supported on dendritic mesoporous silica nanospheres (DMSNs), which exhibit superior peroxidase-like activity, high thermal/long-term stability, and good recyclability. The IrO₂ clusters (1.4 ± 0.2 nm in size) are obtained by the laser ablation without any ligands and possess negative surface charge, which are efficiently loaded on the amino-functionalized DMSNs by electrostatic adsorption. Owing to morphological and structural advantages, the resulted DMSN/IrO₂ heterostructure displays outstanding peroxidase-like catalytic performance. Compared with horseradish peroxidase, it shows comparable affinities but higher reaction rate (2.95 × 10^-7 M·s^-1) towards H₂O₂, resulting from rapid electron transfer during the catalysis. This value is also larger than those of mesoporous silicas supported metal or metal oxides nanoparticles/clusters in the previous studies. Benefitting from excellent peroxidase-catalysis of the DMSN/IrO₂, the colorimetric assays are further successfully established for the detection of acetylcholine esterase and its inhibitor, showing high sensitivity and selectivity. The work provides novel design of supported nanozymes for biosensing.

Broad-Specificity Screening of Pyrethroids Enabled by the Catalytic Function of Human Serum Albumin on Coumarin Hydrolysis

Sensing systems based on cholinesterase and carboxylesterase coupled with different transduction technologies have emerged for pesticide screening owing to their simple operation, fast response, and suitability for on-site analysis. However, the broad spectrum and specificity screening of pyrethroids over organophosphates and carbamates remains an unmet challenge for current enzymatic sensors. Human serum albumin (HSA), a multifunctional protein, can promote various chemical transformations and show a high affinity for pyrethroids, which offer a route for specific and broad-spectrum pyrethroid screening. Herein, for the first time, we evaluated the catalytic hydrolysis function of human serum albumin (HSA) on the coumarin lactone bond and revealed that HSA can act as an enzyme to catalyze the hydrolysis of the coumarin lactone bond. Molecular docking and chemical modifications indicate that lysine 199 and tyrosine 411 serve as the catalytic general base and contribute to most of the catalytic activity. Utilizing this enzymatic activity, a broad specific ratiometric fluorescence pyrethroids sensing system was developed. The binding energetics and binding constants of pesticides and HSA show that pyrethroids bind to HSA more easily than organophosphates and carbamates, which is responsible for the specificity of the sensing system. This study provides a general sensor platform and strategy for screening pesticides and reveals the catalytic activity of HSA on the hydrolysis of the coumarin lactone bond, which may open innovative horizons for the chemical sensing and biomedical applications of HSA.

Dextran-assisted ultrasonic exfoliation of two-dimensional metal-organic frameworks to evaluate acetylcholinesterase activity and inhibitor screening

Acetylcholinesterase (AChE) is regarded as a biomarker of Alzheimer's disease (AD), and its inhibitors show great potential in AD therapy as AChE can increase the neurotoxicity of the amyloid component that induces AD. Because of this, it is crucial and significant to develop a simple and highly sensitive strategy to monitor AChE levels and screen highly efficient AChE inhibitors. Herein, we synthesize an ultrathin two-dimensional (2D) metal-organic framework (MOF) based on copper-catecholate (Cu-CAT) via dextran assisted ultrasound exfoliation, followed by construction of a sensitive sensor for the monitoring AChE and screening of its inhibitors. By adding AChE, the acetylthiocholine (ATCh) substrate is hydrolyzed to be thiocholine (TCh), which decreases the peroxidase-like activity of Cu-CAT nanosheets (Cu-CAT NSs), impairing the signal reaction of 3,3',5,5'-tetramethylbenzidine (TMB) to oxidized-TMB (ox-TMB). In the presence of an AChE inhibitor, the signal can be gradually restored. The newly developed sensor shows high sensitivity and selectivity for AChE and huperzine A (HA, an effective drug for AD, an acetylcholine receptor antagonist), as well as for AD drug discovery from traditional Chinese herbs. The limit of detection of the sensor for AChE is 0.01 mU mL^-1 and the average IC₅₀ value of HA is 30.81 nM under the optimal of catalysis conditions. Compared with the 3D bulk Cu-CAT, the current 2D Cu-CAT NSs exhibit higher peroxidase activity due to more catalytic active site exposure. This study provides a strategy to prepare an ultrathin 2D MOF with high catalytic activity and new insights for the construction of a biosensor to monitor AChE and new AD drugs.

Threaded 3D microfluidic paper analytical device-based ratiometric fluorescent sensor for background-free and visual detection of organophosphorus pesticides

With the increasing concerns of food safety and environmental protection, it is desirable to develop reliable, effective, and portable sensors for detection of organophosphorus pesticides (OPs). Here, a cascade reaction system integrated with threaded 3D microfluidic paper analytical device (3D μPAD) was firstly developed for background-free and visual detection of OPs in agricultural samples. Butyrylcholinesterase (BChE) hydrolyzed acetylcholine into thiocholine (TCh), which reduced MnO₂ nanosheets into Mn²⁺. With addition of OPs, BChE activity was irreversibly inhibited, and the generation of TCh and the reduction of MnO₂ nanosheets were prevented. Then the remaining MnO₂ nanosheets oxidized o-phenylenediamine into 2,3-diaminophenazine with yellow-emission fluorescence, which quenched the fluorescence intensity of red-emission carbon dots (RCDs) via inner-filter effect. Based on above mechanism, a ratiometric fluorescent system was established for OPs detection. Threaded 3D μPAD consisted of 4 layers, which allowed to load and/or add reagents to trigger the cascade reaction system for OPs detection. The fluorescent images presented distinguishable color variations from red to yellow with dichlorvos concentrations ranging from 2.5 to 120 μg L^-1, and the limit of detection was 1.0 μg L^-1. In the practical samples testing, threaded 3D μPAD can eliminate background influence on fluorescent signal for OPs detection. Threaded 3D μPAD integrated with ratiometric sensing platform has merits of accuracy response, facile operation, and background-free detection, which supplies a new alternative approach for on-site pesticide detection.

Advances in Ultra-small Fluorescence Nanoprobes for Detection of Metal Ions, Drugs, Pesticides and Biomarkers

Identification of trace level chemical species (drugs, pesticides, metal ions and biomarkers) plays key role in environmental monitoring. Recently, fluorescence assay has shown significant advances in detecting of trace level drugs, pesticides, metal ions and biomarkers in real samples. Ultra-small nanostructure materials (metal nanoclusters (NCs), quantum dots (QDs) and carbon dots (CDs)) have been integrated with fluorescence spectrometer for sensitive and selective analysis of trace level target analytes in various samples including environmental and biological samples. This review summarizes the properties of metal NCs and ligand chemistry for the fabrication of metal NCs. We also briefly summarized the synthetic routes for the preparation of QDs and CDs. Advances of ultra-small fluorescent nanosensors (NCs, QDs and CDs) for sensing of metal ions, drugs, pesticides and biomarkers in various sample matrices are briefly discussed. Additionally, we discuss the recent challenges and future perspectives of ultra-small materials as fluorescent sensors for assaying of wide variety of target analytes in real samples.

Fluorescent and Colorimetric Ionic Probe Based on Fluorescein for the Rapid and On-Site Detection of Paraquat in Vegetables and the Environment

Detection of pesticide paraquat (PQ) is of considerable significance to ensure food safety, and its rapid and on-site detection is still a challenge. Aimed at the ion characteristics of PQ, an "enrichment and detection" strategy was proposed to improve the sensitivity through electrostatic attractions, and the ion characteristic of probes was adopted to increase the portability through avoiding aggregation-caused quenching effects in the paper strips. Herein, a novel anion-functionalized ionic liquid (IL) probe with a large conjugated plane and rich π-electrons ([Fluo][P₆₆₆₁₄]₂) was designed as a fluorescent and colorimetric dual-channel probe to sensitively and rapidly detect trace amounts of PQ in vegetables and the environment. The proposed probe exhibited good linearity with a detection limit of 64.0 nM in the PQ concentration range of 0.3-7.0 μM (fluorometry) and 0.1 μM in that of 0.1-8.0 μM (colorimetry), respectively. In addition, it displayed a rapid fluorescence quenching response from green to dark (<5 s) and excellent anti-interference (among 23 other pesticides) due to dual effects of electrostatic attraction and π-π stacking. Most importantly, the lipophilic IL probe could be applied in real vegetables and environmental samples with a satisfying recovery rate of 98-103% and assembled into a handy paper strip that achieved the visual semiquantitative detection of PQ. This ionic probe provides a feasible approach for rapidly and conveniently detecting PQ for ensuring agricultural and food safety and opens a new avenue to detect ion-responsive analytes in real complex samples by an "enrichment and detection" strategy.

Nanomaterial-Based Fluorescent Biosensor for Food Safety Analysis

Food safety issues have become a major threat to public health and have garnered considerable attention. Rapid and effective detection methods are crucial for ensuring food safety. Recently, nanostructured fluorescent materials have shown considerable potential for monitoring the quality and safety of food because of their fascinating optical characteristics at the nanoscale. In this review, we first introduce biomaterials and nanomaterials for food safety analysis. Subsequently, we perform a comprehensive analysis of food safety using fluorescent biosensors based on nanomaterials, including mycotoxins, heavy metals, antibiotics, pesticide residues, foodborne pathogens, and illegal additives. Finally, we provide new insights and discuss future approaches for the development of food safety detection, with the aim of improving fluorescence detection methods for the practical application of nanomaterials to ensure food safety and protect human health.

Fluorescent Detection of Two Pesticides Based on CRISPR-Cas12a and Its Application for the Construction of Four Molecular Logic Gates

An intelligent detection platform was developed through molecular logic gate operation based on CRISPR-Cas12a and signal amplification circuits using two kinds of pesticides [acetamiprid (ACE) and atrazine (ATR)] as inputs. The pesticide-aptamer bindings activate the signal amplification process to produce numerous double-stranded DNA, which can be identified by CRISPR-Cas12a. Under the optimal assay conditions, the sensor exhibits excellent analytical performance, with the detection limits for ACE and ATR of 2.5 and 0.2 pM, respectively. The practicality of the platform was verified by testing pesticide concentrations in food samples. Several molecular logic gates (OR, AND, XOR, and INHIBIT) were constructed using "0" and "1" to encode the target pesticides and the fluorescence readout. The logic detection platform with simple operation, high sensitivity, and multiple logic functions is promising to become a powerful sensing system for the intelligent assay of different pesticides in food samples.

Homogeneous photoelectrochemical biosensor for sensitive detection of omethoate via ALP-mediated pesticide assay and Bi2S3@Bi2Sn2O7 heterojunction as photoactive material

A simple homogeneous photoelectrochemical (PEC) sensing platform based on an alkaline phosphatase (ALP)-mediated pesticide assay was established for the sensitive detection of omethoate (OM). The Bi₂S₃@Bi₂Sn₂O₇ heterojunction was used as a photoactive material to provide stable background photocurrent signals. The inhibition of OM on ALP and PEC determination was carried out in the homogeneous system. In the absence of OM, dephosphorylation of L-ascorbic acid 2-phosphate trisodium salt (AAP) was catalyzed by ALP to produce the enzyme-catalyzed product (L-ascorbic acid, AA). AA, as an electron donor, could capture photogenerated holes on the Bi₂S₃@Bi₂Sn₂O₇ heterojunction, thus inhibiting the recombination of electron holes to achieve an increase of the photocurrent signal. When the OM was introduced, the enzyme activity of ALP was reduced due to the organophosphorus pesticides (OPs)-based enzyme inhibition, and the AA produced by catalytic hydrolysis was also reduced, thus reducing the photocurrent signal. Compared with the traditional PEC sensor for OPs, this homogeneous PEC sensor avoided immobilization procedures, covalent labeling, separation, and the steric hindrance effect caused by immobilized biomolecules, which achieved high recognition efficiency and caused a reduction in analysis time. Additionally, an ALP-mediated pesticide assay for the determination of OPs with a simplified experimental process further improved the stability and reproducibility of the PEC sensor. The PEC sensor showed high sensitivity to the target OM within a dynamic range of 0.05 ~ 500 ng mL^-1, and the detection limit was 0.0146 ng mL^-1. Additionally, the PEC biosensing system showed good selectivity and anti-interference ability, and exhibited a satisfactory result in spinach and mustard samples. A homogeneous PEC biosensor based on ALP inhibition strategy was constructed for OM detection in vegetable samples via Bi₂S₃@Bi₂Sn₂O₇ heterojunction as the photoactive substrate material.

Ratiometric fluorescent hydrogel for point-of-care monitoring of organophosphorus pesticide degradation

The residues of organophosphorus pesticides have caused the potential risk in environment and human health, arousing worldwidely great concern. Herein, we fabricated a robust gold nanoclusters/MnO₂ composites-based hydrogel portable kit for accurate monitoring of paraoxon residues and degradation in Chinese cabbages. With the immobilization of gold nanoclusters/MnO₂ composites into a hydrogel, a ratiometric fluorescent signal is generated by catalyzing the oxidation of o-phenylenediamine, which possesses a built-in correction with low background interference. Coupling with acetylcholinesterase catalytic reactions and pesticide inhibition effect, the portable kit can sensitively detect paraoxon residues with a detection limit of 5.0 ng mL^-1. For on-site quantification, the fluorescent color variations of portable kit are converted into digital information that exhibits applicative linear range toward pesticide. Notably, the hydrogel portable kit was successfully applied for precisely monitoring the residue and degradation of paraoxon in Chinese cabbage, providing a potential pathway toward practical point-of-care testing in food safety monitoring.

A Portable Fluorescent Hydrogel-Based Device for On-Site Quantitation of Organophosphorus Pesticides as Low as the Sub-ppb Level

Portable devices possess powerful application prospects in on-site sensing without the limitation of bulky instruments. Given the relevance of pesticides to food safety, we herein fabricated a robust gold nanocluster (AuNC)-based hydrogel test kit for precisely quantified chlorpyrifos by using a three-dimensional (3D) printed subsidiary device. In this work, the fluorescence of AuNC-based hydrogel could be efficiently quenched by cobalt oxyhydroxide nanoflakes (CoOOH NFs) through the Förster resonance energy transfer effect. Chlorpyrifos as an acetylcholinesterase inhibitor controls the enzymatic hydrolysis reaction and further regulates the production of thiocholine that could decompose CoOOH nanoflakes into Co2+, resulting in the fluorescence response of AuNC-based hydrogel. By using a homemade subsidiary device and smartphone, the fluorescence color was transformed into digital information, achieving the on-site quantitative detection of chlorpyrifos with the limit of detection of 0.59 ng ml−1. Owing to specific AuNC signatures and hydrogel encapsulation, the proposed fluorescence hydrogel test kit displayed high sensitivity, good selectivity, and anti-interference capability in a real sample analysis, providing great potential in on-site applications.

Nonenzymatic Target-Driven DNA Nanomachine for Monitoring Malathion Contamination in Living Cells and Bioaccumulation in Foods

Intensive applications of toxic malathion pesticides bring a vital threat to the environment and health. Hence, a credible and sensitive strategy is urgently needed for the respective detection of malathion. In this work, an aptamer-based nonenzymatic autonomous DNA walking machine was fabricated for monitoring trace malathion contamination in cells and foods. Along with the machine walking driven by malathion-triggered reaction entropy, multiple fluorescent signal outputs were thermodynamically generated for signal amplification. The proposed stable DNA nanomachine achieved satisfactory results with a detection limit of 81.9 pg L^-1 for testing malathion, which could be applied to actual samples including apple juice, paddy water, and paddy soil. Furthermore, the high stability, sensitivity, and biocompatibility of the nanomachine enabled monitoring of the malathion contamination in living cells and bioaccumulation in lettuce without additional purification. Consequently, with these excellent performances, it is strongly anticipated that the DNA walking machine has tremendous potential to be extended to general platforms against pesticides to avoid malathion-contaminated agricultural production for environmental safety and human health.

Cysteine Modification of Glutathione-Stabilized Au Nanoclusters to Red-Shift and Enhance the Electrochemiluminescence for Sensitive Bioanalysis

Screening new electrochemiluminescence (ECL) emitters for the design of sensitive detection strategies with even long emission wavelength is intensively anticipated in ECL evolution. Herein, a promising modification strategy for improving the ECL performance of Au nanoclusters (AuNCs) as a water-soluble luminophore was proposed. Upon the introduction of l-cysteine (l-Cys) onto the surface of glutathione (GSH)-stabilized AuNCs (GSH-AuNCs), the dual-thiol bond between l-Cys and GSH was formed to limit the intramolecular motion and nonradiative relaxation of the excited state from the capping agents, which resulted in the enhancement of monochromatic ECL emission of GSH-AuNCs with a red-shifted wavelength. By utilizing triethylamine as a coreactant, the ECL of l-Cys/GSH-AuNCs was about 1.5-fold stronger than that of GSH-AuNCs, and the emission wavelength red-shifted from 660 to 780 nm at a relatively low potential, which could decrease the interference in bioassay and the photochemical damage in nondestructive detection. As a proof of application, a sandwich-type immunosensing method for CYFRA 21-1 was proposed with l-Cys/GSH-AuNCs as the signal tag, which displayed a wide linear ranging from 0.2 fg/mL to 2 ng/mL and a limit of detection down to 0.067 fg/mL at 3S/N. This work provides a wonderful strategy for promoting the performance of ECL emitters.